1. Field of the Invention
The present invention relates to a molded package operating at a high frequency or a high output and, more particularly, to a molded package having an improved heat dissipation effect and improved high-frequency characteristics and capable of performing electrical grounding and heat dissipation separately from each other.
2. Background Art
FIG. 12 shows an example of a conventional molded package operating at a high frequency or a high output (see, for example, Japanese Patent Laid-Open No. 8-213536). As illustrated, thin-film lead electrodes 51 are bent downward to form input/output lead electrodes 52. Also, the thin-film lead electrodes 51 are bent upward to form die pad portions 53 to which a semiconductor chip 54 is bonded, for example, by soldering. The semiconductor chip 54 is connected to the input/output lead electrodes 52 through metal wires 56. The semiconductor chip 54 and the metal wires 56 are encapsulated in a molding material 57 such as a plastic. Some of the lead electrodes 51 are exposed on the die pad portion 53 to form a grounding electrode 55. In this way, the ground inductance is reduced and an improved heat dissipation effect is achieved.
FIG. 13 shows another conventional molded package using thin-film lead electrodes 51 like the above-described one. As illustrated, input/output lead electrodes 52 and a grounding electrode 55 are formed so as to contain a plane common with each other.
In these molded packages, however, the lead electrodes usually have a small thickness of about 0.2 mm and a small heat capacity and, therefore, the heat dissipation effect is low and there is a need for a heat sink of a large heat capacity for limiting the increase in temperature of the semiconductor chip. Also, the high-frequency characteristics cannot be improved because the parasitic inductance and parasitic capacitance are increased.
FIG. 14 is a sectional view of an example of a conventional molded package having an improved heat dissipation effect and improved high-frequency characteristics (see, for example, Japanese Patent Laid-Open No. 4-174547). FIG. 15 is a top view of the molded package shown in FIG. 14. As illustrated, a semiconductor chip 54 is die-bonded to a grounding electrode 58 formed of a thick lead electrode and an upper surface of the grounding electrode 58 is exposed from molding material 57 to improve the heat dissipation effect.
FIG. 16 is a sectional view of another molded package having an improved heat dissipation effect and improved high-frequency characteristics (see, for example, Japanese Patent Laid-Open No. 6-61396).
In the conventional molded packages, however, it is difficult to perform electrical grounding and heat dissipation separately from each other.